The invention relates to systems and methods for CDMA (code division multiple access) paging.
In CDMA systems, a MS (mobile station) accesses the CDMA system on a particular carrier frequency. A single carrier frequency occupies 1.25 MHz in bandwidth, and provides capacity for a number of calls to proceed simultaneously in the same cell. Each carrier has associated with it a single paging channel and a plurality of traffic channels. The channels of a given carrier occupy the same frequency bandwidth and are differentiated from each other by a series of different orthogonal codes.
When a carrier reaches its capacity limit, it is desirable to increase the capacity of the system. One way of achieving this is to increase the number of carriers to greater than one, thereby creating a multi-carrier system.
In existing multi-carrier systems, a MS is capable of tuning to only one of the carrier frequencies at any instant in time. Because of this, the MS is only listening to one of the carrier frequency paging channels. In order to page a MS, the page must be sent on the paging channel of all of the carrier frequencies to ensure that it is sent on the paging channel the MS is listening to. To do this, the page message must be duplicated for each of the paging channels on which the message is to be sent. This results in an inefficient utilization of paging channel resources.
It is an object of the invention to obviate or mitigate one or more of the above identified disadvantages.
According to a first broad aspect, the invention provides in a CDMA (code division multiple access) communications system, a method for a mobile switching centre to send messages to mobile stations within its coverage area, the method first comprising the step of: for each mobile station, maintaining in a form accessible to the mobile switching centre a paging channel identifier which permits an identification of a paging channel the mobile station is monitoring; for each message to be sent to a particular mobile station the method further comprising the steps of: determining on the basis of the paging channel identifier associated with the particular mobile station the particular paging channel that the particular mobile station is monitoring; and broadcasting the message on the particular paging channel.
Preferably, each paging channel identifier comprises a band class and a channel number for the associated mobile station to identify the carrier frequency within the band class that the mobile station is operating or monitoring.
According to a second broad aspect, the invention provides a CDMA basestation transceiver for connection to a basestation controller, the CDMA basestation transceiver being adapted to: 1) include a paging channel identifier permitting the identification of a paging channel that a particular mobile station is monitoring in messages to the basestation controller relating to the particular mobile station; 2) when a message to be sent over the paging channel including said paging channel identifier is received from the basestation controller for transmission to the particular mobile station, identify the paging channel the particular mobile station is monitoring on the basis of the paging channel identifier, and send the message over that paging channel.
According to a third broad aspect, the invention provides a CDMA basestation controller for connection to a mobile switching centre and to a plurality of basestation transceivers, the basestation controller being adapted to: 1) receive a paging channel identifier permitting the identification of a paging channel that a particular mobile station is monitoring in messages received from any basestation transceiver relating to the particular mobile station; 2) include the paging channel identifier in messages to the mobile switching centre relating to the particular mobile station; 3) when a message including said paging channel identifier is received from the mobile switching centre for transmission to the particular mobile station, forward the message including said paging channel identifier to the basestation transceivers.
According to a fourth broad aspect, the invention provides a CDMA mobile switching centre for connection to a basestation controller and adapted to: 1) receive a paging channel identifier permitting the identification of a paging channel that a particular mobile station is monitoring in messages received from the basestation controller relating to the particular mobile station; 2) store the paging channel identifier; and 3) include the paging channel identifier in messages to the basestation controller relating to the particular mobile station.
Advantageously, by monitoring the current frequency that the MS is operating on, for example by monitoring registration messages or handoff messages which have been modified so that they include carrier frequency and bandclass information, the MSC is able to know the current carrier frequency that the MS is operating on. Using this knowledge, the MSC is able to direct the page message to the paging channel for that carrier frequency. In a three carrier CDMA system, this would reduce paging channel usage by a ⅔ (66%). In general, paging channel capacity would be reduced by (nxe2x88x921)/n*100%. In addition, time is saved since the basestation does not need to duplicate the page message for each paging channel.